The NIEHS is conducting an epidemiologic study of uterine fibroids to: (1) compare rates of ultrasound-identified leiomyomas in premenopausal black and white women aged 35 - 49 years, (2) identify risk factors for leiomyomas, and (3) compare biological measurements in leiomyoma tissue and normal myometrium from the same uterus. We will invite a random sample of female members of a prepaid health plan, aged 35 - 49 to participate. Women who show no evidence of fibroids at ultrasound will be compared with a group of cases identified by ultrasound and a group of cases having hysterectomies or myomectomies. This contract with George Washington University Medical Center provides clinical support for this study. Specifically, they will provide logistical support for maintaining a study manager at the medical center, radiology support for ultrasound examinations, OB-GYN support for enrolling surgery participants, pathology support for collecting and processing surgical tissue, and laboratory support for assaying blood lipids. George Washington personnel provide clinical support for identifying any followup needed to diagnose and treat possible medical problems that are found through our study procedures.